JP4170730B2 - Hydrostatic bearing and air spindle motor using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrostatic bearing and an air spindle motor using the same. More specifically, the present invention relates to an air spindle motor used for precision machine tools, precision inspection devices, and the like, and a hydrostatic bearing suitable for the air spindle motor.
[0002]
[Prior art]
A conventional air spindle motor supports a rotating shaft having a thrust collar portion bulging in a disk shape in the radial direction, a radial bearing surface that rotatably supports the outer peripheral surface of the rotating shaft, and both front and rear surfaces of the thrust collar portion. And a motor part disposed on the opposite side of the supported part supported by the bearing part of the rotating shaft (see Patent Document 1 and Patent Document 2).
[0003]
Radial air supply holes for supplying compressed air to the gap with the outer peripheral surface of the rotary shaft are formed on the radial bearing surface, and compressed air is supplied to the gap between the axial bearing surface and the surface of the thrust collar portion. An axial air supply hole is formed. A plurality of radial air supply holes are formed at equal intervals along the circumferential direction of the radial bearing surface, and a plurality of axial air supply holes are formed at equal intervals on a circumference concentric with the rotary shaft on the axial bearing surface. As described above, the radial air supply holes and the axial air supply holes are formed at equal intervals, but no attention is paid to the positional relationship between the radial air supply holes and the axial air supply holes.
[0004]
Manufacturers of air spindle motors have made various efforts to improve their rotational accuracy. On the other hand, the user's demand for the rotational speed of the recent air spindle has increased from the conventional thousands of revolutions / minute to tens of thousands of revolutions / minute. Nano-level accuracy is also required for rotational accuracy (spindle runout).
[0005]
[Patent Document 1]
JP-A-10-96423 [Patent Document 2]
Utility Model Registration No. 2574581 [0006]
[Problems to be solved by the invention]
The present inventor has found that the relationship between the arrangement position of the radial air supply holes and the arrangement position of the axial air supply holes has an influence on the radial rigidity of the bearing as a result of earnest research, and this has improved the rotation accuracy of the air spindle. It became possible to use it. An object of the present invention is to provide an air spindle motor with improved rotational accuracy of the air spindle and a hydrostatic bearing suitable for the air spindle.
[0007]
[Means for Solving the Problems]
The hydrostatic bearing of the present invention is
A radial bearing surface that rotatably supports the outer peripheral surface of the rotating shaft, and an axial bearing surface that supports the thrust collar portion facing the front and rear end surfaces of the thrust collar portion bulging in the radial direction of the rotating shaft; a radial supply hole formed in the circumferential direction at equal intervals in the radial bearing surface, the axial bearing surface, and an axial supply hole formed at regular intervals in sequence circle concentric circumferential direction of the radial supply hole The angle formed by the other one hole between the two holes adjacent to each other in the circumferential direction of the radial air supply hole and the axial air supply hole with respect to the central axis. Is arranged at a central angular position that bisects .
[0008]
With this configuration, when the arrangement of the air supply holes is viewed in the axial direction of the hydrostatic bearing (in front view), the arrangement of the radial air supply holes and the axial air supply holes does not overlap. Furthermore, since one air supply hole becomes the center position of the space | interval of the other air supply hole, the radial rigidity of a bearing is equalized in the circumferential direction. As a result, the rotational accuracy of the rotating shaft supported by the bearing is improved.
[0009]
Further, a static pressure bearing in which a radial radial air supply groove passing through a position of a radial air supply hole formed in the circumferential direction is further formed in the radial bearing surface, and / or in the circumferential direction on the axial bearing surface. A hydrostatic bearing in which an axial air supply groove in the circumferential direction passing through the position of the formed axial air supply hole is formed is preferable. This is because pressure loss in the direction along the circumferential direction of the gas supplied from the air supply hole to the bearing surface is suppressed, and this contributes to uniform radial rigidity.
[0010]
Further, the number of axial air supply holes formed on one circumference is an integral multiple of the number of radial air supply holes formed on one circumference, and each radial air supply hole formed on one circumference is arranged in the circumferential direction. It is also possible to arrange at the central angular position between two adjacent axial air supply holes. Even with this configuration, the radial rigidity can be made uniform.
[0011]
Further, a plurality of radial air supply hole rows in which the same number of radial air supply holes are arranged at equal intervals in the circumferential direction are arranged at intervals in the axial direction of the hydrostatic bearing, and each radial air supply hole is adjacent in the circumferential direction. It can also arrange | position so that it may become a center angle position of two axial air supply holes to perform. Even with this configuration, the radial rigidity can be made uniform.
[0012]
In such a static pressure bearing, the radial air supply hole row is provided with four or more even rows arranged at intervals in the axial direction of the hydrostatic bearing, and the corresponding radial air supply hole of the odd-numbered radial air supply hole row. Are arranged in a straight line in the axial direction of the hydrostatic bearing, and the corresponding radial air supply holes in the even-numbered radial air supply hole array are arranged in a straight line in the axial direction of the hydrostatic bearing. A static pressure bearing in which the radial air supply holes of the air hole row and the radial air supply holes of the even-numbered radial air supply hole row are arranged at different angular positions in the circumferential direction is preferable.
[0013]
The air spindle motor of the present invention is the one of the hydrostatic bearings described above, a rotating shaft that is rotatably supported by the hydrostatic bearing, and a portion of the rotating shaft that is supported by the hydrostatic bearing. And a motor unit disposed on the side.
[0014]
With this configuration, the rotation accuracy of the air spindle is improved.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a hydrostatic bearing and an air spindle motor of the present invention will be described with reference to the accompanying drawings.
[0016]
FIG. 1 shows an air spindle motor 1 used in an apparatus for inspecting a hard disk of a computer, which is an embodiment of the present invention. The air spindle motor 1 includes a motor housing (hereinafter simply referred to as a housing) 2, a bearing member 3 that is fitted and fixed to the inner peripheral surface of the housing 2, and one end side of the air spindle motor 1 that is rotatably supported by the bearing member 3. And the motor unit 5 disposed on the other end side of the rotation shaft 4.
[0017]
The rotary shaft 4 has a large-diameter supported portion 6 whose outer peripheral surface is rotatably supported by the bearing member 3, a small-diameter rotor mounting portion 8 to which the rotor 7 a of the motor unit 5 is attached, and the supported portion 6. In the vicinity of the boundary between the rotor mounting portion 8 and the rotor mounting portion 8, there is a thrust collar portion 9 bulging in a disk shape in the radial direction. An encoder 10 is attached to the tip of the small diameter portion, and a table 18 for attaching a work is attached to the end of the large diameter portion. Reference numeral 7b indicates a stator of the motor.
[0018]
The bearing member 3 includes a radial bearing surface 11 that rotatably supports the outer peripheral surface of the supported portion 6 of the rotating shaft 4 and a pair of axial bearing surfaces 12 that support both front and rear surfaces of the thrust collar portion 9 in the axis L direction. Yes. The bearing member 3 can be separated from the pair of axial bearing surfaces 12 in order to facilitate disassembly and assembly. Therefore, as shown in the figure, the bearing member 3 is composed of two long and short flanged cylindrical members 3a and 3b. As shown in FIG. 2, the housing 2 is also separable from the same part as the bearing member 3 in response to the bearing member 3 being separable.
[0019]
As shown in FIGS. 1 and 2, the radial bearing surface 11 has a plurality of (four in this embodiment) radial air supply holes 13 at regular intervals (90 °) in the circumferential direction. A plurality of (8 in this embodiment) axial air supply holes 14 are formed on each axial bearing surface 12 at equal intervals (45 °) in the circumferential direction toward the gap with the opposing surface of the thrust collar portion 9. Is formed. The axial air supply holes 14 on the front surface of the thrust collar portion 9 and the axial air supply holes 14 on the rear surface (rear surface or back surface) are arranged at the same angular position. An air supply passage 15 for supplying compressed air to all the air supply holes 13, 14 is formed in the housing 2, and the radial air supply holes 13 are arranged on the inner peripheral surface to which the bearing member 3 of the housing 2 is fitted. An air supply channel 15 a communicating with the air supply passage 15 is formed in the circumferential direction. With this configuration, all the air supply holes 13 and 14 communicate with the air supply passage 15, and the air supply passage 15 is connected to an air supply source (not shown).
[0020]
Further, in order to make the rotary shaft support pressure by the air supply as uniform as possible in the circumferential direction of the radial bearing surface 11, all radial air holes 13 (radial air holes described later) are formed in the radial bearing surface 11 in one circumferential direction. A shallow radial air supply groove 16 in the circumferential direction passing through the position of the row) is formed. For the same purpose, the axial bearing surface 12 is formed with a shallow axial air supply groove 17 having a circular outer shape passing through the positions of all the axial air supply holes 14 formed in the circumferential direction. Both of the grooves 16 and 17 have the cross-sectional shape shown in FIG. Compressed air is ejected from the air supply holes 13 and 14 into the gap between the rotary shaft 4 and the bearing surfaces 11 and 12, and the air circulates through the grooves 16 and 17 and escapes to the outside through an exhaust passage 25 described later. Accordingly, the air pressure in the gap is highest at the air supply holes 13 and 14 and decreases as the air holes are separated from each other. However, each of the grooves 16 and 17 has less flow resistance and less pressure loss than the other gaps. In the present invention, the arrangement of the radial air supply holes 13 and the axial air supply holes 14 is devised for the purpose of making the rotation shaft support pressure uniform (making the radial rigidity uniform) as will be described later.
[0021]
The radial air supply groove 16 and the axial air supply groove 17 are formed on the bearing surfaces 11 and 12, but the present invention is not limited to such a configuration. For example, FIG. 8 is a cross-sectional view showing the rotating shaft 4, but as shown here, the air supply grooves 16a are formed on the surface of the rotating shaft 4 (including the surface of the thrust collar portion 9) facing the grooves 16, 17. 17a may be formed, or may be formed on both the rotating shaft 4 and the bearing surfaces 11 and 12. In FIG. 8, reference numeral 26 denotes an air passage for making the recess 18 a (FIG. 1) formed in the table 18 have a positive pressure or a negative pressure.
[0022]
FIG. 3 is a view taken along the line III-III in FIG. 1, and the arrangement of the radial air supply holes 13 and the axial air supply holes 14 will be clarified if FIG. 3 is also referred to. The radial air supply holes 13 are formed in four positions at equal angular intervals (90 °) in the circumferential direction at two positions separated in the axis L direction (FIG. 3). The row of radial air supply holes 13 arranged in the circumferential direction is referred to as a radial air supply hole row. The radial air supply holes 13 of the two spaced apart radial air supply hole arrays are arranged on a straight line parallel to the direction of the axis L (FIGS. 1 and 2). On the other hand, the axial air supply holes 14 are formed at eight positions on the concentric circle with the bearing member 3 at equiangular intervals (45 °) (FIG. 3).
[0023]
Further, as shown in FIG. 3, when the formation positions of these air supply holes 13 and 14 are viewed in the direction of the axis L (front view), the positions of the radial air supply holes 13 are between the axial air supply holes 14 adjacent to each other in the circumferential direction. A central portion between them, that is, a position that bisects the angle formed by the adjacent axial air supply holes 14 with the axis L as the center. In the present embodiment, the number of the radial air supply holes 13 is four and the number of the axial air supply holes 14 is eight, so that the arrangement shown in FIG. 3 is obtained, but both supply like the bearing member 19 shown in FIG. If the number of the air holes 13 and 14 is the same, the air supply holes 13 and 14 are formed at equal angular intervals. In short, regardless of the number of the air supply holes 13 and 14 in the front view, the other of the radial air supply holes 13 and the axial air supply hole 14 disposed between the two adjacent holes in the circumferential direction. It is only necessary that one hole is arranged at the central angular position between the one hole.
[0024]
As described above, the bearing member in which the air supply holes are arranged has a uniform radial rigidity in the circumferential direction as compared with a conventional bearing which does not take such an arrangement. That is, the rotation accuracy of the rotating shaft is improved. The reason for this will be described by comparing the bearing member 3 with an example of a bearing member (comparative example shown in FIG. 11) 51 that does not have the above configuration.
[0025]
In Comparative Example 51, three radial air supply holes 52 are formed at equal angular intervals in the circumferential direction, and four axial air supply holes 53 are formed at equal intervals in the circumferential direction. Then, one radial air supply hole 52 is formed at the same angle as the one axial air supply hole 53 in a front view. The other air supply holes 52 and 53 do not necessarily coincide with each other as illustrated, and the air supply holes 52 and 53 are not evenly spaced from each other. That is, the radial air supply holes (axial air supply holes) arranged between two adjacent axial air supply holes (radial air supply holes) are not arranged at the central angular positions thereof.
[0026]
As a result, the radial rigidity in the circumferential direction of Comparative Example 51 (indicated by the alternate long and short dash line in the graph of FIG. 5) is less uniform than that in Embodiment 3 (indicated by the solid line). The horizontal axis of the graph of FIG. 5 shows the range of 360 ° in the circumferential direction of the radial bearing surface expanded into 16 equal parts (every 22.5 °), and the vertical axis shows the radial rigidity (N / μm). For the embodiment, the dividing points numbered 1 to 16 are numbered in FIG. 3, and for the comparative example, the dividing points numbered 1 to 16 are numbered with respect to FIG. Yes. The radial rigidity is a load value (unit: N) for generating a deflection of 1 μm when a load perpendicular to the axial direction is applied to the rotating shaft. The difference between the embodiment and the comparative example is caused by the supply from the radial supply hole and the supply from the axial supply hole when a load perpendicular to the axial direction is applied to the tip of the rotating shaft. It is thought to be due to the difference in resistance moment.
[0027]
As shown in FIG. 6, when a load W perpendicular to the axial direction is applied to the tip of the rotary shaft, etc., the moment applied to the rotary shaft by the component R that opposes the load direction in the radial supply is the same as the load W The moment applied to the rotating shaft by the axial air supply A at the angular position opposes the moment applied to the rotating shaft by the load W. Therefore, in the case of the comparative example 51, since the radial air supply hole and the axial air supply hole coincide with the position of the number 8, the resistance moment at the position of the number 8 increases, and conversely, the resistance at the positions of the numbers 6 and 10 Since the moment is reduced, the radial rigidity is not uniform as shown in FIG. However, in the case of the embodiment, the radial air supply holes and the axial air supply holes do not overlap at the same angular position, and uniform radial rigidity is obtained as compared with the comparative example.
[0028]
From the above description, it is desirable that the number of radial air supply holes and the number of axial air supply holes are the same from the viewpoint of uniformity of radial rigidity. Further, it is desirable that the number of one of the radial air supply holes and the axial air supply holes is an integral multiple of the other number.
[0029]
FIG. 9 shows another embodiment. The bearing member 23 is different from the above-described bearing member 3 in the arrangement of the air supply holes, and as a result, the arrangement of the air supply passages (not shown) is also different. Since other configurations are common, the same components are denoted by the same reference numerals and description thereof is omitted.
[0030]
In this bearing member 23, radial air supply hole arrays are formed at four positions spaced apart in the axis L direction. In each radial air supply hole row, radial air supply holes 13 are formed at four positions at equal angular intervals (90 °) in the circumferential direction. Of the four radial air supply hole rows spaced apart, the radial air supply holes 13a of the odd-numbered radial air supply hole rows from one end side of the bearing member 23 are arranged on a straight line parallel to the axis L direction. Further, the radial air supply holes 13b of the even-numbered radial air supply hole arrays are also arranged on a straight line parallel to the axis L direction. However, the radial air supply holes 13a of the odd-numbered radial air supply hole arrays and the radial air supply holes 13b of the even-numbered radial air supply hole arrays do not coincide with each other in angular direction, and are shifted by 45 °. Therefore, in the front view, the radial air supply holes 13 are positioned every 45 °. The reason why the radial air supply holes 13 are arranged in this way is to reduce the change in the air pressure in the circumferential direction and to make the radial rigidity uniform.
[0031]
On the other hand, the axial air supply holes 14 are formed at eight positions concentrically with the bearing member 23 at equal angular intervals (45 °). Therefore, in the front view, the radial air supply holes 13 and the axial air supply holes 14 are arranged at equal angular intervals of 22.5 °. As a result, the radial rigidity of the bearing member 23 becomes uniform.
[0032]
In this embodiment, four radial air supply hole arrays are arranged, but the present invention is not limited to this configuration. For example, six or more even number of radial air supply hole arrays may be provided, and the number and arrangement of the axial air supply holes corresponding to the radial air supply holes may be selected so as to meet the above-described idea.
[0033]
The exhaust passage 25 will be described with reference to FIGS. 10 and 3. The compressed air ejected from the air supply holes 13, 14 escapes from the air supply grooves 16, 17 through the gap between the rotary shaft 4 and the bearing surfaces 11, 12, but at this time, most of the compressed air passes through the exhaust passage 25. Escape to the outside. A plurality of (six in this embodiment) radial exhaust holes 27 are formed in the radial bearing surface 11 at equal angular intervals (60 °) in the circumferential direction toward the gap between the rotary shaft 4 and the bearing surfaces 11 and 12. ing. If this is called an exhaust hole row, two exhaust hole rows are formed at intervals in the axis L direction. A radial exhaust groove 28 is formed in the circumferential direction on the outer peripheral surface of the rotating shaft 4 facing each exhaust hole row (see FIG. 8). Of course, instead of the radial exhaust groove 28, or in addition to the radial exhaust groove 28, a radial radial exhaust groove in the circumferential direction may be formed in the portion of the opposing radial bearing surface 11. Further, an exhaust channel 25 a communicating with the exhaust passage 25 is formed on the inner peripheral surface of the housing 2 where the bearing member 3 is fitted in the circumferential direction where the radial exhaust hole 27 is disposed.
[0034]
In addition, axial exhaust holes 29 are formed in the axial bearing surface 12 at equal intervals in the circumferential direction. The axial exhaust hole 29 communicates with the exhaust passage 25.
[0035]
With this configuration, all the exhaust holes 27 and 29 are communicated with the exhaust passage 25, so that the air supply is exhausted to the outside through this path.
[0036]
In the embodiment described above, the number of radial air supply holes in the front view is the same as or less than the number of axial air supply holes, but the present invention is not limited to such a configuration. For example, the bearing may have a larger number of radial air supply holes than the number of axial air supply holes when viewed from the front. What is necessary is just to make it arrange | position to the center angle position of the air supply holes of the one where there are many air supply holes with a smaller number.
[0037]
【The invention's effect】
According to the present invention, the radial rigidity is made uniform along the circumferential direction of the bearing, and as a result, the rotation accuracy of the air spindle is improved.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing an embodiment of an air spindle motor of the present invention.
2 is a longitudinal sectional view showing a part of a bearing member and a housing in the air spindle motor of FIG. 1. FIG.
3 is a view taken along the line III-III in FIG.
FIG. 4 is a view (in front view) seen from the center of an air spindle motor according to another embodiment of the present invention in the axial direction, and corresponds to FIG. 3;
5 is a graph conceptually showing radial stiffness distributions of the bearing member in FIG. 1 and a conventional bearing member (comparative example).
FIG. 6 is a cross-sectional view schematically showing a relationship between a disturbance load applied to a rotating shaft and an air supply force opposed to the disturbance load.
7 is an enlarged view of a VII portion in FIG. 2. FIG.
FIG. 8 is a longitudinal sectional view showing a rotation axis in FIG. 1;
FIG. 9 (a) is a front view showing a bearing member according to another embodiment of the present invention, which corresponds to FIG. 3, and FIG. 9 (b) is a plan view of FIG. 9 (a). FIG. 9C is a cross-sectional view taken along the line AA in FIG. 9A and a cross-sectional view taken along the line BB in FIG. 9B.
10 shows a bearing member and a part of the housing in the air spindle motor of FIG. 1, and is a longitudinal sectional view cut from an angular position different from FIG.
11 is a view seen from the center of a conventional bearing member (comparative example) in the axial direction (front view), and corresponds to FIG. 3. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Air spindle motor 2 ... Housing 3 ... Bearing member 3a, 3b ... Cylindrical member 4 ... Rotating shaft 5 ... Motor part 6 ... Covered Support portion 7a ... Rotor 7b ... Stator 8 ... Rotor mounting portion 9 ... Thrust collar portion 10 ... Encoder 11 ... Radial bearing surface 12 ... Axial bearing surface 13... Radial air supply hole 14... Axial air supply hole 15... Air supply passage 15 a ... Air supply channel 16, 16 a ... Radial air supply groove 17, 17 a. Air supply groove 18... Table 18a... (Recess 19)... Bearing member 23... Bearing member 25. ..Radial exhaust hole 28 ... Radial exhaust groove 29 Axial exhaust hole 51 ... (Comparative Example) bearing member 52 .... (Comparative Example) radial supply hole 53 ... (Comparative Example) axial supply hole

Claims (7)

A radial bearing surface that rotatably supports the outer peripheral surface of the rotating shaft;
An axial bearing surface that supports the thrust collar portion opposite to both front and rear end surfaces of the thrust collar portion that bulges in the radial direction of the rotating shaft;
Radial air supply holes formed at equal intervals in the circumferential direction on the radial bearing surface;
The axial bearing surface, and an axial supply hole formed at equal intervals in a circular peripheral direction of the array concentric with the radial supply hole,
The other one of the radial air holes and the axial air holes arranged between two circumferentially adjacent holes has an angle formed by the one hole with respect to the central axis. A hydrostatic bearing arranged at a central angular position that bisects .   The hydrostatic bearing according to claim 1, wherein a radial radial air supply groove is formed on the radial bearing surface so as to pass through a position of a radial air supply hole formed in the circumferential direction.   The hydrostatic bearing according to claim 1, wherein an axial air supply groove in the circumferential direction passing through a position of an axial air supply hole formed in the circumferential direction is formed on the axial bearing surface.   The number of axial air supply holes formed on one circumference is an integral multiple of the number of radial air supply holes formed on one circumference, and each radial air supply hole formed on one circumference has a circumferential direction. The hydrostatic bearing according to claim 1, wherein the hydrostatic bearing is arranged at a central angular position between two axial air supply holes adjacent to each other.   A plurality of radial air supply hole arrays in which the same number of radial air supply holes are arranged at equal intervals in the circumferential direction are arranged at intervals in the axial direction of the hydrostatic bearing, and each radial air supply hole is adjacent to the circumferential direction. The hydrostatic bearing according to claim 1, wherein the hydrostatic bearing is arranged at a central angular position between two axial air supply holes. Four or more even rows are arranged at intervals in the axial direction of the hydrostatic bearing, in which the same number of radial air holes are arranged at equal intervals in the circumferential direction.
The corresponding radial air supply holes of the odd-numbered radial air supply hole array are arranged in a straight line in the axial direction of the hydrostatic bearing, and the corresponding radial air supply holes of the even-numbered radial air supply hole array are arranged in the axial direction of the hydrostatic bearing. Arranged in a straight line,
The hydrostatic bearing according to claim 5, wherein the radial air supply holes of the odd-numbered radial air supply hole arrays and the radial air supply holes of the even-numbered radial air supply hole arrays are arranged at different angular positions in the circumferential direction.   The hydrostatic bearing according to any one of claims 1 to 6, a rotating shaft rotatably supported by the hydrostatic bearing, and a portion of the rotating shaft opposite to a supported portion by the hydrostatic bearing. An air spindle motor comprising a motor unit disposed on the motor.

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